Tire manufacturing generally involves two basic steps. The first step is building the tire that is yet to be cured into what is termed a “green tire.” Commonly, a “green tire” is made by forming an inner liner and then applying first and second plies or belts around the liner, and then placing a tread overtop the second ply. The second step is to cure the green tire in a tire curing press. The combination of these layers results in a green tire ready for insertion into a tire curing press. The tire curing press includes a toroidally shaped mold that has the desired tread imprinted along the inner toroidal interior space. The green tire is placed inside of the tire curing press and a bladder is placed inside of the green tire. When the bladder is inflated, the green tire is pressed against the inner surface of the tire mold, which is heated to melt and bond the different components of the green tire together.
The most common type of tire curing presses and bladders used are Bag-O-Matic (B.O.M.) type. The bladders have a generally barrel shape with a large empty area inside the center of the bladders, which allows the bladder ends to be clamped to a centerpost column inside of the curing press. The centerpost column operates to stretch the bladders for insertion into a green tire. Further, movement of the centerpost column during the curing process causes the bladders to bow outwards and using steam, water, or gas to inflate the bladder. In the traditional design of the tire curing bladders, the center section of the barrel is larger in diameter than the top and bottom sections of the barrel. These bladders are effective for forming tires having a generally round interior profile.
Tire bladders are fabricated in molds in which the bladder material, such as butyl rubber, is injected into a mold cavity and then allowed to cool. Although the design of bladder molds varies, they generally incorporate a number of common features. The molds generally have outer and inner sections in which the outer section is split into top and bottom portions. After the bladder has been cured and cooled, the top portion of the outer section can be removed and the inner portion can be raised to remove the bladder from the mold. The existing molds are well suited for producing standard types of bladders having a center section that is greater in diameter than the adjacent outer sections.
Currently, however, the demand for alternative types of tire designs is increasing. A tire bladder having a profile known as a “frog eye” is gaining in popularity. A “frog eye” bladder is one where the diameter of the bladder is greater along the shoulder ends of the bladder than at the center section. This configuration leads to a bulging of the upper and lower ends of the cylindrical barrel that generally resembles the bulging eyes of a frog.
The existing bladder molds suffer from many drawbacks in producing these new types of bladders. For example, the existing bladder molds are generally designed to produce a bladder having a center section with a larger diameter than the ends. In addition, the three component design of a two-part outer section and an essentially one-piece inner section of existing bladder molds are ill-suited to the manufacture of a bladder having the “frog eye” geometry.
Accordingly, there is need for an improved bladder mold for the manufacture of “frog eye” geometry bladders.